Mobile electronic devices such as mobile phones, portable digital assistants (PDAs), MP3 players and the like generally include an outer shell, a display screen and a backlight unit. In regular operations, once actions/features are triggered, e.g., by briefly pressing a button, the display screen becomes active. The display screen is illuminated by the backlight unit to display a variety of information such as phone calls, pictures, text messages or the like on the screens. When the mobile device has not been used for a while, it enters a sleep mode and automatically turns off the display. The display screen is still visible, however, which may affect the entire visual effect of the mobile electronic device and is often not desirable.